Fuel cells have been proposed as a power source for electric vehicles and other applications. In proton exchange membrane (PEM) type fuel cells, hydrogen is supplied to the anode of the fuel cell and oxygen is supplied as the oxidant to the cathode. A common technique for storing large quantities of hydrogen is to cool hydrogen via liquefaction techniques and store the liquid phase hydrogen in a cryogenic storage tank. Hydrogen gas liquefies at −253° C. and ambient pressure, and can be stored at about 70g/L in the liquid phase. However, the amount of energy required to convert hydrogen gas into a liquid is very high, and currently may be as much as up to 30% of the energy obtained from using the gas as a fuel.
Conventional hydrogen storage tanks, such as cryogenic tanks used to supply hydrogen gas to a fuel cell, are commonly made of aluminum or stainless-steel alloys. The storage tanks generally consist of an inner storage vessel encapsulated with an outer vessel, or shell, commonly separated from one another with supports (characterized by their low heat conductivity). These types of tanks add excess bulk and weight to a vehicle and may be difficult to incorporate into the overall vehicle design, especially in circumstances when minimal space is available.
Conventional hydrogen storage tanks, such as High-Pressure Vessels for Compressed Gaseous Hydrogen (CGH2) are commonly made of aluminum, stainless-steel alloys (particularly for low pressures applications) or Carbon-Fiber-Composites (particularly for operating pressures greater than 350 bar). Carbon-Fiber-Composite based tanks consist generally of an inner layer, or so called H2 permeation barrier, a layer of carbon fiber as pressure support, and an outer protection shell (usually made of KEVLAR®, or a related material such as glass fibers). At 700 bar and room temperature, the density of hydrogen gas is about one half of the value of liquid hydrogen at 1 bar and 20 K. Additionally, CGH2 at operating pressures greater than 200 bar shows deviations from the ideal gas law: The H2 density no longer increases in proportion to the operating pressure. Due to the fact that conventional pressure vessels typically feature a cylindrical form, CGH2 tanks are difficult to incorporate into the overall vehicle design, especially in circumstances when minimal space is available.
Accordingly, there is a need for an improved hydrogen storage vessel. In particular, one that minimizes weight and conserves space within a motor vehicle while providing the required storage capabilities necessary for the operation of a power generating device such as a fuel cell or an internal combustion engine.